8GB Memory has nothing to do with your C Drive. A 1TB hard drive is rather difficult to fill if you don't have a huge music, movie, picture library. I'm talking HUGE picture library. You'd have to have hundreds of thousands of songs to fill 1TB. What do you have on your hard drive that could be taking up so much space?
Secondly, what is the model of desktop? Sometimes, they have little 24GB solid state drives in them just for your operating system, and those will fill up very fast. Give us a model number of desktop and we can help you better.